In a conventional automobile, a block heater is a standalone accessory used to heat the coolant fluid inside the engine block or in any area of the coolant circuit. This device is mostly used in geographic regions with cold temperatures because heating the engine coolant can ease starting an engine.
The operation of an engine block heater, however, can disturb the on-board diagnostics (OBD) of rationality of temperature sensors, thus, there is a need for a method for detecting a presence of a block heater in an automobile.
Prior art methods for determining engine malfunctions have tried to determine whether a block heater is present and has been used by checking for a temperature difference between the engine coolant and the intake manifold air or ambient temperature, when the engine has been stopped for a minimum period; other methods have tried to determine the presence of the block heater by checking for a temperature drop in the engine coolant temperature after a period of time after engine start.
U.S. Pat. No. 6,931,865B1 describes a method and apparatus for determining coolant temperature rationality in a motor vehicle. U.S. Pat. No. 7,975,536B2 describes a method to detect the presence of a liquid-cooled engine supplemental heater. U.S. Pat. No. 8,140,246B1 describes a method and system for detecting a presence of a block heater in an automobile. U.S. Pat. No. 7,757,649B2 describes a controller, cooling system abnormality diagnosis device and block heater determination device of the internal combustion engine.
The methods of detection of a block heater used by the prior art are not reliable enough or cannot be used under certain circumstances. In case the coolant temperature sensor has a fault, detectable by OBD monitors, all the detection methods developed on prior art that rely only on this sensor cannot be used. In case the engine is equipped with an electronic controlled thermostat valve or a forced circulation block heater, that will allow the coolant fluid to circulate over the entire cooling circuit, allowing a homogenous distribution of the temperature on the system, the detection methods based on a drop of the coolant temperature after engine start are not always reliable, as the coolant temperature might not drop, since the coolant temperature on the system was homogeneously distributed. On both circumstances the methods of detection developed on the prior art are not able to guarantee a reliable detection of the block heater.
Because the problems with the prior art are present on more advanced engines which use electronic controlled thermostat valves, which allow the coolant fluid to flow through all the coolant circuit independent of the coolant fluid temperature, these valves are yet only used on few engines because they were developed recently, on the next years they might become common on several engines.
The problem is also present on engines that are equipped with forced circulation block heaters, which usually have a pump to force the coolant to flow through the system in order to have a better or more homogeneous temperature distribution on the coolant circuit, which will also prevent the prior art to detect the presence of a block heater.
The conventional methods are dependent on the relative position of the engine coolant temperature sensor relative to the block heater. However, these conventional methods can be inadequate depending on the configuration of the automobile and/or the placement of the block heater.